Parity Dominoes

Tiles are dealt from a shuffled double-six set. One extra tile is flipped face-up at random to start the line.

On your turn, play a tile from your hand against either open end, but the touching number must share parity with that end: odd on odd, even on even. Doubles always match, since both halves share the same parity.

You bank the sum of the two open ends after you place your tile — but only if the two ends have opposite parity, one odd and one even. If both ends are odd, or both even, the turn scores nothing. The pill beside the turn indicator always shows which the board currently is.

This makes each placement a choice rather than a formality. Scoring needs a tile that changes the ends' relationship: on a same-parity board you need a mixed tile (one odd half, one even), and on an opposite-parity board a solid one (both halves alike). Playing for nothing is sometimes right, since whatever you leave showing is what your opponent scores against next.

When both halves of a tile are legal against the end you chose, you decide which faces outward. The prompt shows what each is worth to you now; the cost of the higher one is what it hands over.

No legal tile in hand? Tap Swap tile, then tap the tile you want to send back. A playable tile comes out of the pile in its place, so your hand size never changes and you still play this turn. If nothing in the pile can help, your turn is skipped instead.

Emptying your hand doesn't end the game by itself — the other player keeps playing out their hand. The game ends once both players have either emptied their hand or run out of legal moves with nothing playable left in the pile.

Anyone still holding tiles at the end subtracts the pip total of their hand from their score. Highest score wins.

The line snakes to fit the table — tiles turn from horizontal to vertical at the edge of the board, just like laying real dominoes around a tight table.